Field of the Disclosure
The teachings in accordance with the exemplary embodiments of this present disclosure generally relate to a pre-charging circuit of inverter.
Description of Related Art
In general, an inverter is a power converting device configured to convert an inputted AC electric power to DC electric power having a predetermined frequency and voltage. FIG. 1 is a circuit diagram illustrating an inverter according to prior art.
Referring to FIG. 1, an inverter (200) converts a 3-phase AC power to a DC power through a rectifier (210) by receiving the 3-phase AC power from a 3-phase electric power source (100), stores the power in a DC-link capacitor (230), converts the DC power to an AC power having a predetermined frequency through an inverter unit (240) and supplies the AC power to a 3-phase motor (300).
The inverter (200) is a VVVF (Variable Voltage Variable Frequency) system, and controls the speed of the motor (300) by varying the voltage and frequency in response to a PWM (Pulse Width Modulation) output. The inverter system thus mentioned is applied with a pre-charging circuit (220).
The pre-charging circuit (220) serves to prevent an over-current generated by an inrush current inputted to the inverter (200) and also prevent dielectric breakdown of elements. A pre-charging resistor (221) of the pre-charging circuit (220) is operated only when an initial power of the inverter (200) is inputted, and prevents an unnecessary power loss of charging resistor by diverting a current flow to a relay (222) in a normal state.
FIG. 2 is a detailed circuit diagram illustrating the pre-charging circuit (220) and a DC-link capacitor (230).
Referring to FIG. 2, an input current is transmitted in the order of a node P1, a node P1 and DCP node through the rectifier (210). At this time, the node P1 and the node P2 are connected via a conductor.
In case of current path at the pre-charging circuit, a current is transmitted through the pre-charging resistor (221), and the current is transmitted through the relay (222) at the normal operation. That is, the current path is formed by the pre-charging resistor (221), the node DCP and the DC-link capacitor (230) at the pre-charging, and formed by the relay (222), the node DCP and the DC-link capacitor (230) at the normal operation. The current path at the normal operation performs an over-current protection, because a current flows from the node DCP to a node DCPI through a shunt resistor (231) when an over-current including arm shoot-through is generated.
However, because the pre-charging resistor (221) is connected between the nodes P2 and DCP in the above circuit, only one path exists where a current must pass the node DCP at the pre-charging. Thus, the current must pass the node DCP, and as a result, a considerable limited obstacle is generated when the pre-charging circuit is designed on a printed circuit board (PCB).